import java.util.Scanner;



/**

   Counts the number of digits with value 7 in the decimal 

   representation of the integer n

*/

public class CountSevens

{

   public static void main(String[] args)

   {

      Scanner in = new Scanner(System.in);

      int n = in.nextInt();



      // your work here

      String s = String.valueOf(n);

      int count = 0;

      for(int i=0;i<s.length();i++){

          if(s.charAt(i) == '7'){

              count++;

          }

      }

      System.out.println(count);

   }

}

